1. Field of the Invention
The present invention relates to a magnetic field generator for an MRI, a packing member for the magnetic field generator for the MRI, and a method for packing the magnetic field generator for the MRI. More Specifically, the present invention relates to a magnetic field generator for MRI incorporating permanent magnets, a packing member for such a magnetic field generator for MRI, and a method for packing said magnetic field generator for MRI.
2. Description of the Prior Art
A magnetic field generator for MRI using permanent magnets is becoming popular in recent years. The magnets used in such an apparatus have a very strong magnetism. For this reason, the magnetic field generator for MRI must be protected during transportation so that no magnetic objects such as tools are drawn into a magnetic circuit built in the magnetic field generator. Typically, the entire magnetic field generator is concealed into a wooden box during the transportation as shown in FIG. 11.
However, packing the entire magnetic field generator is a major, time-consuming job.
Another trend in the recent years is that an increasing number of magnetic field generators for MRI have an open type structure in which the number of column yokes are decreased for improved psychological comfort of a patient. In this open type magnetic field generator however, even a very small misalignment (such as 0.05 mm) between an upper plate yoke and a lower plate yoke will result in an ununiform magnetic field, adversely affecting an image obtained by the MRI apparatus.
A problem is that this open type magnetic field generator for MRI is so heavy (typically 15 tons), that an open region of the generator main body can be easily deformed by craning operation or by vibration during transportation. This results in dimensional changes in the magnetic circuit (particularly in a distance between upper and lower pole pieces), deteriorating the uniformity of the magnetic field. Therefore, after arriving at a site of installation, a long time has to be spent for re-adjusting the uniformity of the magnetic field.